(a) Field of the Invention
This invention relates to the finishing of annular articles, such as rings, cylinders and the like, and the invention in particular but not exclusively relates to the finishing of annular seals such as brush seals for sealing a rotatable shaft to a housing therefor.
The term "annular" as used herein when referring to the article to be finished is intended to extend to articles having shapes bound by two similar concentric curviform figures, such as elipses, as well as truly circular shapes bound by two concentric circles.
(b) Description of the Prior Art
A lathe is a known form of apparatus for finishing annular articles, in which the article is held between two rotatable members arranged co-axially, and a cutting tool is caused to remove material from the article as it rotates. The cutting tool may be replaced by a grinding wheel when high quality surface finishes are required. It is however often difficult to hold an annular article in a lathe and complex jigs may have to be specially provided. Then, production is low, and it can take several minutes to align each article ready for machining. To overcome these problems, centreless grinding machines are known, but in the case of an annular article having a relatively short axial length it can still be most difficult to hold the article sufficiently reliably to obtain an accurately finished article. Particularly in the case of a brush seal having a plurality of metallic bristles projecting from an annular carrier, the holding of the seal sufficiently firmly so as to be able to perform a finishing operation on the carrier or on the bristles themselves can be most troublesome.